At a certain stage of their processing, the wafer disks introduced into the fabrication process are cut into approximately circular disks. For various reasons, which include the crystalline orientation in the plane of the disk, on the one hand, and the arrangement of markings applied, e.g., in the outer area of the wafer disks, on the other hand, it is necessary to position a batch of wafer disks in a harmonized manner in relation to their azimuthal alignment. This is carried out when the wafer disks are arranged on a device standing next to each other. Even though a device and a process in which the wafer disks are positioned lying azimuthally one on top of another, e.g., in the reaction chamber, are also known from U.S. Pat. No. 6,052,913, this has essential drawbacks, which are due to the fact that very fine particles present in the air or gas flowing through will not settle on the wafer disks, on the one hand, and an azimuthal positioning is to be preferred in the case of the vertical arrangement of the wafer disks in respect to the processing operations to be performed before and thereafter, on the other hand.
For the harmonized positioning, the wafer disks are provided with a notch in the outer circumference. This notch may be either in the form of an approximately triangular incision or in the form of a circular segment-shaped incision.
U.S. Pat. No. 5,533,243 discloses a device and a corresponding process in which vertically arranged wafer disks are arranged on a drive roller and another roller, over which a plurality of small free-running wheels are pulled. The azimuthal harmonization of the individual notches is performed corresponding to the suggestion according to U.S. Pat. No. 5,533,243 such that the circular segment-shaped notches prevent the movement of the wafer disks by the drive roller when the notches arrive at the drive roller. The wafer disks are then rotated together into the desired position with another driven roller (notch moving roller). However, this process has numerous drawbacks. On the one hand, wafer disks with circular segment-shaped incisions are necessary for the device, which is not always the case in practice. On the other hand, the process is, however, liable to fault due to the plurality of driven rollers and the change in the height position of the wafer disks during the different phases of alignment and it is not beneficial to the wafer disk due to the generation of particles by the drive rollers.
U.S. Pat. No. 5,662,452 discloses a device in which an aligning bar is rotated by a drive roller and the wafer disks arranged in the vertical position are now rotated until the likewise circular segment-shaped notches snap into the aligning bar, which is smaller than they are, so that no further rotation is possible. This device also has technical drawbacks, because, on the one hand, only wafer disks with circular segment-shaped notches can again be positioned and, on the other hand, the device is designed such that the aligning bars will rotate further in the notches and generate friction, which produce abraded particles, until the operation is terminated and all wafer disks are aligned. Furthermore, this device likewise has the drawback that the height of the wafer disks will change during the aligning operation due to snapping in. Furthermore, the drawback that a slow phase, which should be avoided, must be provided to ensure the reliability of the snapping in is essential.
A process similar to the above-mentioned two processes is also known in U.S. Pat. No. 5,853,284, in which the force transmission is stopped by a slight change in height during the snapping in of the driven roller into the—necessarily circular segment-shaped—notches by the force transmission to the roller being designed as a slip clutch. Besides the above-mentioned drawbacks in terms of a change in height, this also leads to abraded particles, which shall be avoided according to the present invention.
U.S. Pat. No. 5,970,818 discloses a device that is already capable, in principle, of positioning wafer disks with triangular notches, but without overcoming the drawbacks of the above-mentioned state of the art, because the lowering of the wafer disks is likewise made use of, but the wafer disks will then drop so low that a braking means provided especially for this purpose prevents the further rotation of the wafer disks, doing so, however, again at the expense of slipping of the drive roller on the wafer disk.
It is already known from the above-mentioned U.S. Pat. No. 5,533,243 that the position of the notches is checked with an optical sensor, but the sensor is used there only to determine whether or not the notches of all wafer disks are in the same position, namely, in one row, through which the optical beam can pass.